Willcox, AZ, USA
N233TR
Robinson R-44 II
The pilot executed an emergency landing after experiencing a drive belt failure. During cruise flight, the alternator light illuminated and the ammeter showed a drop. The pilot turned off all nonessential electrical equipment. The pilot heard a "thump," which was followed by the smell of burnt rubber. About 15 seconds later, the clutch light illuminated and the pilot heard a "thud." The pilot lowered the collective and both lights continued to illuminate. The pilot then entered an autorotation and pulled the clutch circuit breaker. As the helicopter settled from the flare, it contacted a "clump" of dirt. The helicopter tipped forward, which bent the forward portion of the skids, and resulted in the main rotor striking the tail boom. No preimpact anomalies with either the airframe or engine were discovered. The main rotor drive belts were found in the drive compartment in a shredded condition. The alternator belt was not recovered. I
On April 2, 2003, about 0800 mountain standard time, a Robinson R-44 II, N233TR, collided with terrain during an autorotative forced landing after experiencing a drive belt failure near Willcox, Arizona. The owner was operating the helicopter under the provisions of 14 CFR Part 91. The helicopter sustained substantial damage. The commercial pilot and one passenger were not injured. The cross-country ferry flight departed Tucson, Arizona, about 0700, en route to St. Louis, Missouri. Day visual meteorological conditions prevailed, and no flight plan had been filed. In a telephone interview with the National Transportation Safety Board investigator, the pilot reported that the purpose of the flight was to fly the newly purchased helicopter to St. Louis. The new owner accompanied the pilot. The pilot stated that he was acting as pilot-in-command for the flight because of the new owner's limited flight time in the make and model. During cruise flight, the alternator light illuminated and the ammeter showed a drop. The pilot turned off all nonessential electrical equipment. The pilot heard a "thump," which was followed by the smell of burnt rubber. About 15 seconds later, the clutch light illuminated and the pilot heard a "thud." The pilot lowered the collective and both lights continued to illuminate. The pilot then entered an autorotation and pulled the clutch circuit breaker. As the helicopter settled from the flare, it contacted a "clump" of dirt. The helicopter tipped forward, which bent the forward portion of the skids, and the main rotor struck the tail boom. The Safety Board investigator and a representative from the helicopter's manufacturer examined the helicopter at Robinson Helicopter Company, Torrance, California. No preimpact anomalies with either the airframe or engine were discovered. The main drive belts were located in the drive compartment around the engine main rotor drive, forward of the drive pulley. The belts exhibited shredding. The position of the adjustment bolt and the adjustment slot on the alternator were measured and compared to positions on similar helicopters. The measurements were consistent with recommended positions by the manufacturer. The aft plate on the alternator exhibited rub marks in a circular pattern, outside of the path of pulley rotation. The alternator belt was not recovered. In a telephone conversation with the Safety Board investigator, the Robinson representative stated that the cooling fan on the helicopter pulls air over the top of the engine and that air is then released as it blows aft, over the bottom of the engine. The alternator is positioned in the path of the outward airflow.
The failure of the alternator belt which resulted in the failure of the main drive belt.
Source: NTSB Aviation Accident Database
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